NIST Conducts Experiments on Impact of Coordinating Suppression with Ventilation
October 13, 2015
NVFC Chairman visits test site
By Daniel Madrzykowski
Over the course of the past 50 years the technology and protective equipment available to firefighters has changed dramatically. New materials have been introduced into firefighters’ protective clothing and equipment that has a higher resistance to heat than canvas and denim. The use and continued development of self-contained breathing apparatus (SCBA) has made working in a smoke filled building safer.
These improvements have enabled firefighters to work in fire environments that previous generations could not due to exposure to heat and toxic gases. As a result, interior attack tactics have become the norm. Unfortunately the rate of traumatic firefighter fatalities on the fireground, as reported by the National Fire Protection Association, have increased from 1.8 per 100,000 structure fires in the late 1970s to 3.0 per 100,000 fires in 2008. Why would this happen during a period when firefighters have access to the best equipment and training they have ever had?
There may be several reasons for the trend in fireground fatalities. Since the 1970s the number of structure fires in the United States has decreased by more than 50 percent. So on average, firefighters have less experience on the fireground. In addition, conditions on the fireground have changed. Modern building construction methods and the materials have improved the livability and energy efficiency of our homes, but these engineered materials can increase the severity of a structure fire due to their design and fuel composition relative to the fire performance of natural legacy materials. As a result firefighters today are likely to respond to a fuel rich fire environment inside a well-insulated structure that has limited capacity to withstand the thermal insult from a free burning fire. Providing additional oxygen to a structure filled with hot unburned fuel gases (smoke) may result in a rapid increase in fire size.
For these reasons, the National Institute of Standards and Technology (NIST) has been conducting research to examine both the capabilities of equipment and tactics used by firefighters. For the past two generations of firefighters, suppression operations have been conducted primarily from the interior of the structure as a means to reduce water damage, manage the “thermal balance,” and limit fire damage to structures. In current training manuals it is stated that these operations must be coordinated with the ventilation operations. However guidance on fire control and coordination has been limited.
Previous research and examinations of line-of-duty deaths have shown that ventilation events occurring with firefighters in the structure prior to suppression have led to tragic results. One means of reducing the possibilities of this occurrence would be to begin to extinguish the fire prior to entering the structure. In effect, this would be an offensive exterior fire attack where water is directed into the structure from the exterior with a solid stream or a straight stream to cool the fire gases and reduce the heat release rate of the fire, prior to the firefighters entering the building. The major concern with this type of operation is the potential harm that might occur to people trapped in the structure or the amount of water damage to the structure. Therefore, measurements are needed to document the changes of the thermal environment within the structure and the impact on the viability of people who might be trapped in the structure.
In the summer of 2015, NIST conducted experiments which focused on the importance and impact of coordinating suppression with ventilation. These experiments are a culmination of more than 10 years of real scale fire experiments conducted with fire departments across the United States.
On August 6, National Volunteer Fire Council (NVFC) Chairman Kevin D. Quinn visited the NIST test site in Delaware County, PA. Quinn, along with representatives from the Boston Fire Department, Philadelphia Fire Department, and the Fire Department City of New York, had the opportunity to witness two experiments in a two-story townhouse type structure. The lower level of the structure was intended to represent a walk-out basement with wood interior finish. The fires in each experiment were started on a sofa in the lower level. The upper level of the structure was connected to the basement via a stairway with the door at the top of the stairs open. Each floor of the structure had an area of approximately 720 square feet.
In both experiments, the upper level door on Side A of the structure was opened and then placed in a partially closed or control position (14-inch opening). This “door control” was done to limit the flow velocity through the upper level. The difference between the experiments was the timing of the application of water into the “basement” fire compartment after the walkout doors were opened or vented.
|Upper level A Side Door fully opened, then moved to a door control position.|
The order of events for each experiment began with ignition of a sofa against the Side A wall of the lower level. The fire was allowed to develop until it became ventilation limited or “fuel rich,” due to a reduction in the oxygen concentration on the lower level. At this point the Side A door on the upper level was fully opened for 30 seconds and then was moved to a “control position” or partially closed with an open gap of 14 inches. The door remained in this position for the remainder of the experiment.
After the flow conditions upstairs stabilized, the lower level doors on Side C were opened. In the first experiment, 150 gpm straight stream was directed through the Side C doorway into the fire compartment within seconds of the doors being opened. In the second experiment, the application of water was delayed.
Experiment 1, coordinated attack. In this experiment, the highest gas temperatures that the helmets, face pieces, and other instrumented gear on the upper level near the top of the stairs were exposed to was 200°F. Heat flux and gas velocity exposures were also relatively low for a protected firefighter; both were below 10 kW/m2 and 10 mph respectively. Gas concentrations were at lethal levels for unprotected civilians in the lower level and at the top of the stairs, prior to the lower level doors being opened. After flowing water into the fire room for about 30 seconds, the temperatures throughout the structure decreased, as did the heat flux and gas velocity. The oxygen levels began to increase while the carbon dioxide and carbon monoxide decreased. After Experiment 1, there was no visible damage to the fire helmets, SCBA face pieces, and other gear.
Experiment 1, hose stream application coordinated with the ventilation of the fire room, coordination prevents flashover in the basement.
|Firefighter Safety Equipment at the top of the stairs after Experiment 1.|
Experiment 2, suppression delayed after ventilation. In this test, venting the fire room took place well ahead of fire suppression, and as a result the energy level throughout the structure was significantly higher. After the basement transitioned through flashover, the gas temperatures in the area of the helmets and face pieces were approximately 1000°F. Heat flux and gas velocity exposures where higher than those in Experiment 1. Heat flux peaked at approximately 50 kW/m2 and gas velocities higher than 10 mph. As a result the helmets and face pieces reached temperatures of 800°F and higher on their exterior while the interior temperatures were in excess of 400°F. This experiment generated thermal conditions that resulted in visible damage to the equipment and which would likely have resulted in death or serious injury to any firefighter caught in that position.
Experiment 2, water application delayed after venting the fire compartment, allowed flashover to occur.
|Firefighter Safety Equipment at the top of the stairs after Experiment 2.|
A full report on all of these experiments is being prepared by NIST. The testing of the gear was supported in part with funding from the U.S. Fire Administration.
Based on a review of NIOSH investigation reports from the past 15 years, it is clear that fires with rapidly developing or changing flow paths are a significant hazard to the fire service. The development of (or changes to) a flow path could be caused by the failure of a component of the structure, such as a door, window, or portion of a ceiling, wall, or floor. Environmental conditions such as wind can generate hazardous thermal conditions within a flow path. Uncoordinated ventilation procedures can also be the cause of increased thermal hazards within a flow path. The experiment where the line was delayed following the ventilation of the basement generated conditions representative of these types of dramatic change in the exhaust portion of the flow path.
Fire suppression efforts should be coordinated with interior operations and ventilation procedures to reduce thermal hazards related to flow paths within a structure. Ongoing research by NIST, Underwriters Laboratories (UL), and others has demonstrated that applying water from the exterior into the fire area of a structure (typically prior to the start of interior operations) can significantly improve the safety of firefighters by reducing the thermal hazard from the fire and reducing the potential for developing high velocity hot gas flows within the structure. For a listing of free online training links see www.nist.gov/fire.
Perhaps adding exterior attack, essentially a tactic from the “old days,” to your tactical toolbox would be valuable to both your firefighters’ safety and effectiveness.
Daniel Madrzykowski, PE, FSFPE, is a fire protection engineer and the Leader of the Fire Fighting Technology Group at NIST. The group’s focus is improving firefighter safety and effectiveness. Dan has worked with many fire organizations to transfer his research results into practice. He is a member of the NFPA Fire Service Training Committee. He is also a member of the International Society of Fire Service Instructors and was named their Instructor of the Year in 2009. Dan holds the rank of Honorary Battalion Chief with the Fire Department of New York City and received the IFSTA Granito Award for Excellence in Fire Leadership in 2012. In 2013 Dan was invited to the White House in honor of receiving a Service to America Medal. He received a President’s Award from the International Association of Fire Chiefs for his firefighting research in 2014.
*Photos courtesy of NIST.